Among the falsesocial mediaposts published during the hack were some made in the name of the Emir of Qatar, in which he appeared to make disparaging remarks about US President Donald Trump, praised Gaza's Hamas leaders and expressed support for Iran as an "Islamic power".

"The Washington Post story today that we actually hacked the Qataris is also not true", he told the London-based think-tank Chatham House. This was followed nearly immediately by a trade embargo and the closing of all air, land and see borders to Qatar, effectively leaving Qatar in its current isolated state.

The Post gave no further details of how American intelligence had reached its conclusion, but it had previously been alleged that some of the boycotting countries could be behind a hack of the Qatar news agency.

It was unclear whether the UAE carried out the hacks itself or had contracted to have them done, the Postsaid.

The United Arab Emirates warned Qatar on Monday it could not belong to the Gulf Cooperation Council if it undermined regional security, calling for a "change of behaviour" but not "regime change". Funding, supporting, and enabling extremists from the Taliban to Hamas and Gaddafi.

UAE Ambassador to the U.S. Yousef al-Otaiba denied the new information in a statement, saying it was "false".

A senior UAE official said worldwide monitoring was needed in the standoff between Qatar and its Arab neighbours, adding he saw signs that the pressure exerted on Doha "was working". "Inciting violence, encouraging radicalization, and undermining the stability of its neighbors", he added.

Washington and Doha signed the agreement as US Secretary of State Rex Tillerson visited Qatar on a three-day tour of Persian Gulf-Arab countries to try to end a month-long rift between Western-allied Arab states. Staunchly defending its innocence against the allegations from the onset of the crisis, Qatar claimed the demands were deliberately created to be impossible for it to meet and rejected them, causing the current stalemate in negotiations.